One type of semiconductor junction device that emits radiation is a diode laser. A semiconductor diode laser can be formed in a monocrystalline rectangular parallelepiped semiconductor body having a PN junction lying between two spaced parallel major surfaces. Two mutually parallel reflective faces that are perpendicular to the PN junction form a laser cavity adjacent one side of the PN junction. Lasing action is produced by applying a forward voltage across the PN junction. The forward bias injects electrons across the PN junction to stimulate emission of the radiation. Above a given level of electron injection, called threshold current, (J.sub.TH), emitted radiation is collected and amplified in the laser cavity. The amplified radiation exits the laser cavity parallel the PN junction as a monochromatic coherent beam.
In order to apply the forward bias across the PN junction, ohmic contacts are made to the semiconductor material on opposite sides of the PN junction. Lead-salt semiconductors are useful in making diode lasers operating in the infrared region of the spectrum. In making diode lasers from lead-salt semiconductors, there are difficulties in obtaining suitable ohmic contacts to the P-type material. The contacts are too high in electrical resistance as formed or if low enough as formed, subsequently increase in resistance to objectionable levels. Indium is a highly desirable contact metal from a mechanical standpoint for lead-salt lasers. In fact, it has proven to be quite satisfactory in making durable low resistance ohmic contacts to N-type lead-salt surfaces. However, it did not produce durable contacts on P-type lead-salts. I have now found how to use indium to consistently obtain highly satisfactory ohmic contacts on not only P type but even N type lead-salt semiconductors. Not only does one obtain the desirable mechanical attributes of indium but one can also consistently initially obtain low contact resistance and the contact resistance remains low over extended time periods. Accordingly, they are more durable. Such durability is important to a laser diode. However, it is also important to a diode that emits light non-coherently, for example an infrared light emitting diode (LED) operating near or above room temperature. Maintaining low contact resistance on a LED is important too, particularly since one would want to operate it at room temperature or above.